The invention relates to a device for introducing gas into a liquid which is contained in a tank or similar container. The invention relates more particularly to such a device which is especially suitable for the oxygen treatment of water containing sewage sludge or similar waste products, which would be normally reacted with oxygen as part of the purification thereof. The gas to be introduced, for this application, may be oxygen or an oxygen containing gaseous substance. It is, however, not intended to limit the invention to sewage treatment applications nor to oxygen or oxygen containing gaseous substances.
An especially advantageous feature of the instant invention permits recirculation of gaseous substances which pass out of the liquid, back into the gas supply to the device introducing the gaseous substance into the liquid.
There are a number of methods and devices at present in use for operations such as waste water sludge purification, wherein the material to be treated is aerated. Those methods which utilize a closed tank normally teach aeration by means of a hollow shafted stirrer through which the gas can flow into the liquid, or by means of surface mounted impellers. Such devices and methods are known, for example, from the German disclosures AS 2,032,480 and OS 2,146,403.
In any operation, the tank closure must meet certain requirements in order to ensure the non-objectionable operation of the aerating device. Some of these are:
The closure must at least provide a substantially gas-tight seal to prevent the loss of gases from the tank. The closure must be easily removable to permit cleaning of the tank. Corrosion resistance of the cover material is another important feature, in terms of maintenance of the device. Finally, the closure must be able to withstand the pressure of the expanding volume of the gas which forms above the liquid, as a result of the gases being introduced into the liquid and percolating up and out of the liquid level. This last feature not only ensures the gas-tight integrity of the device, but also enables oxygen recycling, by a gas withdrawal device disposed above the liquid for re-introducing the oxygen, thereby permitting more efficient use of oxygen which has passed unreacted through the liquid.